On 19 February, flight controllers were in the process of updating the International Space Station's command and control software when a communications fault related to this transition occured. During the transition from primary computer to the backup computer as part of the software load procedure, there was a loss of all communications with mission control at 1435 GMT. The back up computer was not letting the station communicate with Nasa's Tracking and Data Relay Satellites, Normal ommunications and telemetry were restored at 1934 GMT using another computer. In the intervening period a secondary radio voice communications were able to made as the station passsed over Russian ground stations.
International Space Station - Courtesy: NASA